Liquid crystal panel substrate, liquid crystal panel, and electronic device and projection display device using the same

ABSTRACT

In a liquid crystal substrate in which a matrix of reflecting electrodes is formed on a substrate, a transistor is formed corresponding to each reflective electrode and a voltage is applied to the reflective electrode through the transistor. A silicon oxide film having a thickness of 500 to 2,000 angstroms is used as the passivation film and the thickness is set to a value in response to the wavelength of the incident light to maintain a substantially constant reflectance.

This is a Continuation of application Ser. No. 11/152,163 filed Jun. 15,2005, now U.S. Pat. No. 7,158,205, which in turn is a Divisional ofapplication Ser. No. 10/021,012, filed Dec. 19, 2001, now U.S. Pat. No.6,933,996, which in turn is a Divisional of application Ser. No.08/955,461, filed Oct. 21, 1997, granted on Feb. 5, 2002, as U.S. Pat.No. 6,344,888 B2. The disclosures of the prior applications are herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to liquid crystal panels and liquidcrystal panels, and in particular, a technology suitable for activematrix liquid crystal panels in which pixel electrodes are switched withswitching elements formed on a semiconductor substrate or an insulatingsubstrate. The present invention also relates to an electronic deviceand a projection display device using the same.

2. Description of Related Art

Liquid crystal panels having a structure in which a thin film transistor(TFT) array using amorphous silicon is formed on a glass substrate havebeen conventionally used as reflective active matrix liquid crystalpanels which are used in light valves of projection display devices.

The active matrix liquid crystal panel using the TFT is a transmissiveliquid crystal panel, and a pixel electrode is formed with a transparentconductive film. In transmissive liquid crystal panels, since theswitching element-forming region, such as a TFT, which is provided ineach pixel is not a transparent region, it has a serious defect that theaperture ratio is low and decreases as the resolution of the panel isimproved to XGA, or S-VGA.

As a liquid crystal panel having a smaller size than the transmissiveactive matrix liquid crystal panel, a reflective active matrix liquidcrystal panel in which pixel electrodes, as reflecting electrodes, areswitched with transistors formed on a semiconductor substrate or aninsulating substrate has been proposed.

In such a reflective liquid crystal panel, the formation of apassivation film as a protective film on the substrate in which thereflecting electrodes are formed is often omitted since it is not alwaysnecessary. The present inventor has studied the formation of apassivation film on a reflective liquid crystal panel substrate.

In general, a silicon nitride film formed by a low pressure CVD processor a plasma CVD process is often used as a passivation film insemiconductor devices. The passivation film formed by a current CVDprocess inevitably has some variation of the thickness of approximately10%. Accordingly, the reflective liquid crystal panel has disadvantages,e.g. the reflectance noticeably varies with variation of the thicknessof the passivation film.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a reflective liquidcrystal panel substrate and a liquid crystal panel having a passivationfilm which does not vary the refractive index of the liquid crystal andhaving high reliability.

It is another object of the present invention to provide a reflectiveliquid crystal panel having high reliability and excellent image qualityand an electronic device and projection display device using the same.

The present invention for achieving the above object has a liquidcrystal panel substrate comprising a matrix of reflective electrodesformed on a substrate, a transistor formed corresponding to eachreflective electrode, a voltage applied to the reflective electrodesthrough the respective transistors, a passivation film formed on thereflecting electrodes, the passivation film having a thickness tocontrol a change in reflectance of the reflecting electrodes towavelengths of incident light to within approximately 1%, and thus thethickness is selected such that the variation of the thickness lessaffects the reflectance of the reflecting electrodes.

A phenomenon in which reflectance on the electrodes significantly varieswith the wavelength of light can be suppressed by forming thepassivation film with a silicon oxide film.

A silicon oxide film having a thickness of 500 to 2,000 angstroms isused as the passivation film of the liquid crystal panel substrate.Although the silicon oxide film has a function as a protective filmslightly inferior to the silicon nitride film, it less affects thereflectance of the pixel electrode due to variation of the filmthickness compared to the silicon nitride film. Since a silicon oxidefilm having a thickness of 500 to 2,000 angstroms shows particularlyslight dependency of the reflectance on the wavelength, the use of thesilicon oxide film as the passivation film can reduce variation of thereflectance.

Further, the thickness of the passivation film is set to an adequaterange in response to the wavelengths of incident light on eachreflecting electrode. In detail, the thickness of the silicon oxide filmas the passivation film is 900 to 1,200 angstroms for a pixel electrodereflecting blue light, 1,200 to 1,600 angstroms for a pixel electrodereflecting green light, or 1,300 to 1,900 angstroms for a pixelelectrode reflecting red light. When the thickness of the silicon oxidefilm as the passivation film is set to the above range, variation of thereflectance for each color can be suppressed to 1% or less, reliabilityof the liquid crystal panel is improved and the image quality isimproved in a projection display device using the reflecting liquidcrystal panel as a light valve.

It is preferred that the thickness of the silicon oxide film as thepassivation film be determined in consideration of the thickness of analignment film formed thereon. In this case, the alignment film has athickness of preferably 300 to 1,400 angstroms, and more preferably 800to 1,400 angstroms. Variation of the refractive index of the liquidcrystal can be effectively suppressed by setting the thickness of thealignment film to the above-mentioned range.

In a liquid crystal panel having a pixel region in which a matrix ofpixel electrodes are disposed and peripheral circuits, such as a shiftregister and a control circuit, formed on the same substrate, apassivation film composed of a silicon oxide film may be formed abovethe pixel region and a passivation film composed of a silicon nitridefilm may be formed above the peripheral circuits. Since the thickness ofthe passivation film above the peripheral circuits does not affect thereflectance, the use of the silicon nitride film enables secureprotection of the peripheral circuits and improvement in reliability.

A silicon nitride film may be provided as an insulating interlayerbetween the reflecting electrodes and the metal layer thereunder,instead of the formation of the passivation film on the reflectingelectrodes or by using together with the passivation film composed ofthe silicon oxide film. The moisture resistance is thereby improved andthe MOSFET for pixel switching and the holding capacitor can beprevented from corrosion due to water or the like.

A monolithic protective structure in which a silicon nitride film formedon a passivation film of a silicon oxide is provided over the edge andthe side wall of the laminate of the transistor for switching the pixel,and the insulating interlayer and metal layer which form a wire regionsupplying a given voltage and signal to the transistor. The water proofproperty is thereby improved at the edge of the liquid crystal panel inwhich water could otherwise readily penetrate, and the durability isalso improved since it acts as a reinforcing material.

When a liquid crystal panel using the above-mentioned liquid crystalpanel substrate is used in a light valve of a projection display device,a color separation means for separating the light from a light sourceinto three primaries, a first reflective liquid crystal panel formodulating red light from the color separation means, a secondreflective liquid crystal panel for modulating green light from thecolor separation means and a third reflective liquid crystal panel formodulating blue light from the color separation means are provided, thethickness of the silicon oxide film forming a passivation film of thefirst reflective liquid crystal panel is in a range of 1,300 to 1,900angstroms, the thickness of the silicon oxide film forming a passivationfilm of the second reflective liquid crystal panel is in a range of1,200 to 1,600 angstroms, and the thickness of the silicon oxide filmforming a passivation film of the third reflective liquid crystal panelis in a range of 900 to 1,200 angstroms, the passivation film has athickness in response to the wavelength of the color light to bemodulated in each light valve for modulating each color light. Variationof the reflectance and variation of the synthetic light thereforedecrease. Variation of hue of the color display in the projected lightbetween different projection display device products is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) is a cross-sectional view of a first embodiment ofa pixel region of a reflecting electrode side substrate of a reflectiveliquid crystal panel in accordance with the present invention.

FIG. 2 is a cross-sectional view of an embodiment of a structure of aperipheral circuit of a reflecting electrode side substrate of areflective liquid crystal panel in accordance with the presentinvention.

FIG. 3 is a planar layout of a first embodiment of a pixel region of areflecting electrode side substrate of a reflective liquid crystal panelin accordance with the present invention.

FIG. 4 is a cross-sectional view of an embodiment of an edge structureof a reflecting electrode side substrate of a reflective liquid crystalpanel in accordance with the present invention.

FIG. 5 is a cross-sectional view of another embodiment of a reflectingelectrode side substrate of a reflective liquid crystal panel inaccordance with the present invention.

FIG. 6 is a plan view of an example of a layout of a reflectingelectrode side substrate of a reflective liquid crystal panel in anembodiment.

FIG. 7 is a cross-sectional view of an embodiment of a reflective liquidcrystal panel using a liquid crystal panel substrate of an embodiment.

FIG. 8 is a graph including a gate driving waveform and a data linedriving waveform of a FET for pixel electrode switching of a reflectiveliquid crystal panel in accordance with the present invention.

FIG. 9 is a block diagram of a video projector as an example ofprojection display devices in which a reflective liquid crystal panel ofan embodiment is used as a light valve.

FIG. 10 is a graph illustrating that the reflectance of a reflectingelectrode composed of an aluminum layer varies with the thickness of thesilicon oxide film at a given length of the incident light.

FIG. 11 is a graph illustrating that the reflectance of a reflectingelectrode composed of an aluminum layer varies with the thickness of thesilicon oxide film at a given length of the incident light.

FIG. 12 is a graph in which the reflectance is plotted at a givenwavelength interval when the thickness of the silicon oxide film ischanged within a wavelength range covering blue light.

FIG. 13 is a graph in which the reflectance is plotted at a givenwavelength interval when the thickness of the silicon oxide film ischanged within a wavelength range covering green light.

FIG. 14 is a graph in which the reflectance is plotted at a givenwavelength interval when the thickness of the silicon oxide film ischanged within a wavelength range covering red light.

FIGS. 15 (a), (b) and (c) are appearances of electronic devices usingreflection liquid crystal panels in accordance with the presentinvention, respectively.

FIG. 16 is a cross-sectional view of another embodiment of a reflectingelectrode side substrate of a reflective liquid crystal panel inaccordance with the present invention.

FIG. 17 is a cross-sectional view of another embodiment of a reflectingelectrode side substrate of a reflective liquid crystal panel inaccordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will nowbe described with reference to the drawings.

FIGS. 1( a), 1(b) and 3 show a first embodiment of a reflectingelectrode substrate of a reflective liquid crystal panel in accordancewith the present invention. FIGS. 1( a), 1(b) and 3 are across-sectional view and a planar layout view, respectively, of onepixel section among a matrix of pixels. FIG. 1( a) is a cross-sectionalview taken along cross-section line I-I of FIG. 3. FIG. 1( b) is across-sectional view taken along cross-section line II-II of FIG. 3.FIG. 6 is an entire planar layout view of a reflecting electrodesubstrate of a reflective liquid crystal panel in accordance with thepresent invention.

In FIGS. 1( a) and 1(b), identification numeral 1 represents a P-typesemiconductor substrate such as single-crystal silicon (or N-typesemiconductor substrate (N⁻⁻)), identification numeral 2 represents aP-type well region having an impurity content higher than that of thesemiconductor substrate formed on the surface of the semiconductorsubstrate 1, and identification numeral 3 represents a field oxide filmfor separating elements (so called LOCOS) formed on the surface of thesemiconductor substrate 1. The well region 2 is formed as a common wellregion of a pixel region in which a matrix of pixels of, for example,768 by 1,024 is provided, and is not limited to this. As shown in FIG.6, the well region 2 is separately formed from a well region in whichperipheral circuits, such as a data line driving circuit 21, a gate linedriving circuit 22, an input circuit 23 and a timing control circuit 24,which are disposed on the periphery of a pixel region 20 in which amatrix of pixels are arranged, are formed. The field oxide film 3 isformed into a thickness of 5,000 to 7,000 angstroms by selective thermaloxidation.

Two openings per pixel are formed in the field oxide film 3. In thecenter of one opening a gate electrode 4 a composed of polysilicon ormetal silicide is formed through a gate oxide film (insulating film) 4 bformed by thermal oxidation, source and drain regions 5 a and 5 bcomposed of N-type impurity doping layers (hereinafter referred to asdoping layers) are formed on the substrate surface at both sides of thegate electrode 4 a, and a MOSFET is thereby formed. The gate electrode 4a extends to the scanning direction (pixel line direction) to form agate line 4.

On the substrate surface in the other opening formed in the field oxidefilm 3, a P-type doping region 8 is formed. On the surface of the P-typedoping region 8, an electrode 9 a composed of polysilicon or metalsilicide is formed through an insulating film 9 b formed by thermaloxidation. A capacitor for holding a voltage applied to the pixel isformed between the electrode 9 a and the P-type doping region 8 throughthe insulating film 9. The electrode 9 a and the polysilicon or metalsilicide layer as the gate electrode 4 a of the MOSFET can be formed bythe same process, and the insulating film 9 b under the electrode 9 aand the insulating film as the gate insulating film 4 b can be formed bythe same process.

The insulating films 4 b and 9 b are formed on the semiconductorsubstrate surface in the openings by thermal oxidation into a thicknessof 400 to 800 angstroms. The electrodes 4 a and 9 a have a structure inwhich a poly-silicon layer having a thickness of 1,000 to 2,000angstroms is formed and a silicide layer of a high boiling point metalsuch as Mo or W having a thickness of 1,000 to 3,000 angstroms is formedthereon. The source and drain regions 5 a and 5 b are formed by means ofself-alignment by implanting an N-type impurity on the substrate surfaceat both sides of the gate electrode 4 a as a mask by ion implanting. Thewell region just below the gate electrode 4 a acts as the channel region5 c of the MOSFET.

The above-mentioned P-type doping region 8 is formed by, for example, adoping treatment including exclusive ion implanting and heat treatment,and may be formed by ion implanting before the formation of the gateelectrode. That is, after the insulating films 4 b and 9 b are formed,an impurity of the same conductivity type as the well is implanted toform a region 8 on the well surface having a higher impurityconcentration and a lower resistance than those in the well. Theconcentration of impurities in the well region 2 is preferably1×10¹⁷/cm³ or less, and more preferably 1×10¹⁶/cm³ to 5×10¹⁶/cm³. Thepreferred concentration of the surface impurities in the source anddrain regions 5 a and 5 b is 1×10²⁰/cm³ to 3×10²⁰/cm³. Also, theconcentration of the P-type doping region 8 is preferably 1×10¹⁸/cm³ to5×10¹⁹/cm³, and more preferably 1×10¹⁸/cm³ to 1×10¹⁹/cm³ in view ofreliability of the insulating film forming the holding capacitance andvoltage resistance.

A first insulating layer 6 is formed over the electrodes 4 a and 9 a onthe field oxide film 3, a data line 7 (refer to FIG. 3) substantiallyconsisting of aluminum is formed on the insulating film 6, and a sourceelectrode 7 a and an auxiliary bonding wire 10 are provided so as toprotruded from the data line. The source electrode 7 a is electricallyconnected to the source region 5 a through a contact hole 6 a formed inthe insulating film 6, one end of the auxiliary bonding wire 10 iselectrically connected to the drain region 5 b through a contact hole 6b formed in the insulating film 6 and the other end is electricallyconnected to the electrode 9 a through a contact hole 6 c formed in theinsulating film 6.

The insulating film 6 is formed by, for example, depositing an HTO film(a silicon oxide film formed by a high temperature CVD process) having athickness of approximately 1,000 angstroms and depositing a BPSG film (asilicate glass film containing boron and phosphorus) having a thicknessof approximately 8,000 to 10,000 angstroms. The metal layer which formsthe source electrode 7 a (the data line 7) and the auxiliary bondingwire 10 has, for example, a four-layer structure of Ti/TiN/Al/TiN fromthe bottom. The thicknesses of the lower Ti layer, TiN layer, Al layerand upper Ti layer are 100 to 600 angstroms, approximately 1,000angstroms, 4,000 to 10,000 angstroms and 300 to 600 angstroms,respectively.

A second insulating interlayer 11 is formed over the source electrode 7a, the auxiliary bonding wire 10 and the insulating interlayer 6, and alight shielding film comprising a second metal layer 12 composed ofaluminum is formed on the second insulating interlayer 11. The secondmetal layer 12 as the light shielding film is formed as a metal layerfor forming bonding wires between devices in the peripheral circuits,such as a driving circuit, which are formed on the periphery of thepixel region, as described below. No additional step is thereforerequired for forming only the light shielding film 12, and the processcan be simplified. The light shielding film 12 is formed so as to coverthe entire pixel region 20 and has an opening 12 a on the auxiliarybonding wire 10 for piercing a pillar connecting plug 15 whichelectrically connects a pixel electrode with a MOSFET described later.That is, in the plan view shown in FIG. 3, a rectangular frame 12 arepresents the above-mentioned opening and the entire outside of theopening 12 a is covered with the light shielding film 12. The incidentlight from the upper side in FIG. 1 (the liquid crystal layer side) isalmost completely shielded and a light leakage current flow due to lighttransmission in the channel region 5 c and the well region 2 of theMOSFET for pixel switching can be prevented.

The second insulating layer 11 is formed by, for example, depositing asilicon oxide film by a plasma CVD process using TEOS(tetraethylorthosilicate) (herein after referred to as a TEOS film) intoa thickness of approximately 3,000 to 6,000 angstroms, depositing a SOGfilm (a spin-on-glass film), etching it by an etch-back process, anddepositing a second TEOS film thereon into a thickness of approximately2,000 to 5,000 angstroms. The second metal layer 12 as the lightshielding film may have the same structure as the first metal layers 7(7 a) and 10, and may have, for example, a four layer structure ofTi/TiN/Al/TiN from the bottom. The thicknesses of the lower Ti layer,TiN layer, Al layer and upper Ti layer are 100 to 600 angstroms,approximately 1,000 angstroms, 4,000 to 10,000 angstroms and 300 to 600angstroms, respectively.

In this embodiment, a third insulating layer 13 is formed on the lightshielding layer 12, and a rectangular pixel electrode 14 as a reflectiveelectrode almost corresponding to one pixel is formed on the thirdinsulating layer 13 as shown in FIG. 3. A contact hole 16 is providedinside the opening 12 in the light shielding film 12 so as to pierce thethird insulating interlayer 13 and the second insulating interlayer 11,and the contact hole 16 is filled with a pillar connecting plug 15composed of a high melting point metal, such as tungsten, whichelectrically connects the auxiliary bonding wire 10 and the pixelelectrode 14. A passivation film 17 is formed on the entire pixelelectrode 14.

When forming a liquid crystal panel, an alignment film is formed on asubstrate at the reflective electrode side, an opposing substrate whichis provided with an opposing (common) electrode therein and an alignmentfilm thereon is provided on the inside face at a given gap so as to facethe substrate, and a liquid crystal is encapsulated into the gap.

For example, after tungsten is deposited by a CVD process to form theconnecting plug 15, the tungsten and the third insulating interlayer 13are planarized by a chemical mechanical polishing (CMP) process, thepixel electrode 14 is formed by a low temperature sputtering processusing aluminum into a thickness of 300 to 5,000 angstroms and is formedby a patterning process into a square having a side of approximately 15to 20 μm. The connecting plug 15 may be formed by smoothing the thirdinsulating interlayer 13 by a CMP process, providing the contact holeand depositing tungsten therein. The passivation film 17 is composed ofa silicon oxide film having a thickness of 500 to 2,000 angstroms in thepixel region and a silicon nitride film having a thickness of 2,000 to10,000 angstroms in the scribe section. A seal section represents aregion which is formed by a sealing material for fixing the gap betweenthe two substrates in the liquid crystal. The scribe section representsa section along a scribe region, i.e., the edge of the liquid crystalpanel substrate, when a number of reflective liquid crystal panelsubstrates are formed in a semiconductor wafer and separated alongscribe lines into semiconductor chips.

The use of a silicon oxide film as the passivation film 17 covering thepixel region can prevent a significant change in a reflectance due tothe variation of the film thickness and the wavelength of the light.

On the other hand, the passivation film 17 covering a region outside theregion in which the liquid crystal is encapsulated (outside the sealsection) is formed of a single-layer structure consisting of a siliconnitride film or a double-layer structure consisting of a silicon oxidefilm and a silicon nitride film thereon in order to further improvereliability, in which the silicon nitride film is superior to thesilicon oxide film in terms of water proof property. Although water canreadily penetrate from the peripheral region of the substrate contactingto the outer atmosphere and in particular the scribe section, thesilicon nitride protective film covering the region can further improvethe reliability and durability at the region.

A polyimide alignment film is formed on the entire passivation film 17and subjected to rubbing treatment to form a liquid crystal panel.

The thickness of the passivation film 17 can be determined within anadequate range in response to the wavelength of the incident light. Thethickness of the silicon oxide as the passivation film is in a range of900 to 1,200 angstroms for a pixel electrode reflecting blue light,1,200 to 1,600 angstroms for a pixel electrode reflecting green light,or 1,300 to 1,900 angstroms for a pixel electrode reflecting red light.A thickness of the silicon oxide film as the passivation film set towithin the range can suppress the variation of the reflectance in thereflective electrode composed of aluminum to 1% or less. The ground isillustrated below.

FIGS. 10 and 11 show the results of dependency of the reflectance of thealuminum reflective electrode on the thickness of the silicon oxide filmat different wavelengths. In FIG. 10, symbol ⋄ represents reflectance ata thickness of 500 angstroms, symbol □ represents reflectance at athickness of 1,000 angstroms, symbol Δ represents reflectance at athickness of 1,500 angstroms, and symbol x represents reflectance at athickness of 2,000 angstroms. In FIG. 11, symbol ⋄ representsreflectance at a thickness of 1,000 angstroms, symbol □ representsreflectance at a thickness of 2,000 angstroms, symbol Δ representsreflectance at a thickness of 4,000 angstroms, and symbol x representsreflectance at a thickness of 8,000 angstroms.

As shown in FIG. 11, at a thickness of 4,000 angstroms the reflectancedecreases approximately 3% from 0.89 to 0.86 as the wavelength changesfrom 450 nm to 550 nm and the reflectance decreases approximately 8%from 0.85 to 0.77 as the wavelength changes from 700 nm to 800 nm. At athickness of 8,000 angstroms the reflectance decreases approximately 3%from 0.89 to 0.86 as the wavelength changes from 500 nm to 600 nm andthe reflectance decreases approximately 6% from 0.86 to 0.80 as thewavelength changes from 650 nm to 750 nm. In contrast, no significantchanges are observed at a thickness of 500 angstroms, 1,000 angstroms,1,500 angstroms or 2,000 angstroms. These results illustrate that theeffective thickness of the silicon oxide film is in a range of 500 to2,000 angstroms.

As a result, a reflective liquid crystal panel having a reduceddependency of the reflectance on the wavelength can be achieved by athickness of 500 to 2,000 angstroms as the passivation film formed onthe reflective electrode.

FIGS. 10 and 11 also demonstrate that the reflectance slightly changesin a specified thickness range of the silicon oxide film. The presentinventor further studied an optimum thickness range of the silicon oxidefilm for the incident and reflecting color light. The results are shownin FIGS. 12 to 14. FIG. 12 is a graph illustrating reflectances atvarious thicknesses of the silicon oxide film in a wavelength range of420 to 520 nm for blue light and its neighbor, FIG. 13 is a graphillustrating reflectances at various thicknesses of the silicon oxidefilm in a wavelength range of 500 to 600 nm for green light and itsneighbor, and FIG. 14 is a graph illustrating reflectances at variousthicknesses of the silicon oxide film in a wavelength range of 560 to660 nm for red light and its neighbor.

FIG. 12 demonstrates that at a thickness of 800 angstroms thereflectance decreases by approximately 1.1% from 0.896 to 0.882 as thewavelength changes from 440 nm to 500 nm. At a thickness of 1,300angstroms, the reflectance changes by approximately 0.6% from 0.887 to0.893 as the wavelength changes from 420 nm to 470 nm and thereflectance is noticeably lower than those at other thicknesses within awavelength of 420 to 450 nm. In contrast, no significant changes inreflectance are observed and a satisfactorily high reflectance isachieved at a thickness of 900 angstroms, 1,000 angstroms, 1,100angstroms or 1,200 angstroms.

As shown in FIG. 13, at a thickness of 1,100 angstroms the reflectancedecreases by approximately 1.6% from 0.882 to 0.866 as the wavelengthchanges from 550 nm to 600 nm. At a thickness of 1,700 angstroms thereflectance is considerably lower than those at other thicknesses withina wavelength of 500 nm to 530 nm. In contrast, no significant changes inreflectance are observed and a satisfactorily high reflectance isachieved at a thickness of 1,250 angstroms, 1,400 angstroms or 1,550angstroms.

As shown in FIG. 14, at a thickness of 1,200 angstroms the reflectancedecreases by approximately 3.4% from 0.882 to 0.848 as the wavelengthchanges from 560 nm to 660 nm. At a thickness of 2,000 angstroms thereflectance is considerably lower than at other thicknesses within awavelength of 560 nm to 610 nm. In contrast, no significant changes inreflectance are observed and a satisfactorily high reflectance isachieved at a thickness of 1,400 angstroms, 1,600 angstroms or 1,800angstroms.

FIGS. 12 to 14 demonstrate that when a thickness of the silicon oxidefilm as the passivation film is set to within the range of 900 to 1,200angstroms for a pixel electrode which reflects blue light, 1,200 to1,600 angstroms for a pixel electrode which reflects green light or1,300 to 1,900 angstroms for a pixel electrode which reflects red light,the variation of the reflectance for each color can be suppressed to 1%or less and a satisfactorily high reflectance can be achieved.

Each of the graphs shown in FIGS. 12 to 14 shows the reflectance when apolyimide alignment film is formed with a thickness of 1,100 angstromson the passivation film. The optimum thickness range of the siliconoxide film slightly shifts with a different thickness of the alignmentfilm. Regarding the thickness range of the alignment film, it is notcapable of aligning if its thickness is less than 300 angstroms in viewof suppressing the variation of reflectance, whereas the polyimideabsorbs high wavelength light and low wavelength light and hasappreciable capacitance which is connected in series to the liquidcrystal capacitor in the equivalent circuit; therefore it is preferredthat the thickness of the alignment film be within a range of 300 to1,400 angstroms. If a decrease in the alignment capability due to adecreased thickness of the alignment film is anticipated, the thicknessis preferably in a range of 800 to 1,400 angstroms.

When the thickness of the alignment film is within the above-mentionedrange and the thickness of the silicon oxide film in the liquid crystalpanel for each color is within the above-mentioned range, the variationof the reflectance can be satisfactorily suppressed to 1% or less.

Accordingly, when a color display is formed in one liquid crystal panel,the thickness of the passivation film on the reflective electrode can bevaried according to the color of each pixel. That is, in a configurationwhere an RGB color filter is formed on the inner face of the opposingsubstrate facing the reflective substrate in response to pixelelectrodes and the color light passing through the color filter isreflected from the pixel electrode, a single plate-type reflectiveliquid crystal panel having high reflectance can be obtained by setting,the thickness of the passivation film formed on the pixel electrodereflecting red light from the red (R) color filter to 1,300 to 1,900angstroms, the thickness of the passivation film formed on the pixelelectrode reflecting green light from the green (G) color filter to1,200 to 1,600 angstroms and the thickness of the passivation filmformed on the pixel electrode reflecting blue light from the blue (B)color filter to 900 to 1,200 angstroms. The liquid crystal panel canalso be used as a light valve for a single plate-type projection displaydevice. The color light may be formed by a means which converts lightincident on each pixel electrode into the color light, for example, adichroic mirror, instead of the color filter.

The liquid crystal panel in accordance with the present invention canalso be used in a projection display device described later which isprovided with a liquid crystal panel reflecting red light, a liquidcrystal panel reflecting green light and a liquid crystal panelreflecting blue light. In this case, it is preferred that thethicknesses of the silicon oxide film as the passivation film be in arange of 1,300 to 1,900 angstroms for the liquid crystal panel in thelight valve for modulating red light, in a range of 1,200 to 1,600angstroms for the liquid crystal panel in the light valve for modulatinggreen light, and in a range of 900 to 1,200 angstroms for the liquidcrystal panel in the light valve for modulating blue light,respectively.

FIG. 3 is a planar layout view of the liquid crystal substrate at thereflection side shown in FIG. 1. As shown in FIG. 3, the data line 7 andthe gate line 4 are formed so as to cross each other in this embodiment.Since the gate line 4 is formed so as to act as the gate electrode 4 a,the hatched region H of the gate line 4 in FIG. 3 acts as the gateelectrode 4 a and a channel region 5 c of MOSFET for pixel switching isprovided on the substrate surface thereunder. The source and drainregions 5 a and 5 b are formed on the substrate surface at both sides(at the upper and lower sides in FIG. 3) of the channel region Sc. Thesource electrode 7 a connecting to the data line is formed so as toprotrude from the data line 7, extended along the vertical direction inFIG. 3, and is connected to the source region 5 a of the MOSFET throughthe contact hole 6 b.

The P-type doping region as a constituent of one terminal of the holdingcapacitor is formed so as to link to the P-type doping region in theadjacent pixel in the direction parallel to the gate line 4 (the pixelline direction). It is connected to a power line 70 provided outside thepixel region through contact holes 71 so that a given voltage V_(ss),such as 0 volt (ground voltage), is applied. The given voltage V_(ss)may be close to a voltage of the common electrode provided on theopposing substrate, a central voltage of the amplitude of image signalssupplied to close to the data line, or an intermediate voltage betweenthe common electrode voltage and the amplitude central voltage of theimage signals.

The connection of the P-type doping region 8 to the voltage V_(ss) atthe outside of the pixel region stabilizes the voltage of one electrodeof the holding capacitor and the holding voltage held in the holdingcapacitor during the non-selection time period of the pixel (thenon-leading time of the MOSFET), and decreases the variation of thevoltage applied to the pixel electrode during one frame time period.Since the P-type doping region 8 is provided near the MOSFET and thevoltage of the P-type well is simultaneously fixed, the substratevoltage of the MOSFET is stabilized and the variation of a thresholdvoltage due to the back gate effect can be prevented.

Although not shown in the drawings, the power line 70 is also used as aline which supplies a given voltage V_(ss) as a well voltage to theP-type well region (separated from the well of the pixel region) in theperipheral circuit provided outside the pixel region. The power line 70is formed of the first metal layer which is the same as the data line 7.

Each pixel electrode 14 has a rectangular shape and is provided in closeproximity to the adjacent pixel electrode 14 at a given distance, forexample, 1 μm, so as to decrease the light leaked between the pixelelectrodes as much as possible. Although the center of the pixelelectrode is shifted from the center of the contact hole in thedrawings, it is preferable that both centers substantially agree witheach other due to the following reason. Since the second metal layer 12having a light shielding effect has an opening 12 a at the periphery ofthe contact hole 16, the opening 12 a provided near the edge of thepixel electrode 14 causes random reflection between the second metallayer 12 and the back surface of the pixel electrode of the lightincident from the gap between the pixel electrodes in which the lightreaches the opening 12 a and leaks from the opening through the lowersubstrate. It is therefore preferable that the center of the pixelelectrode and the center of the contact hole 16 substantially agree witheach other, because the distance in which the light incident from thegap with the adjacent pixel reaches the contact hole is almost equalizedat the edge of each pixel electrode and the light barely reaches thecontact hole which will form the light incident on the substrate side.

Although the above-mentioned embodiment includes the N-channel-typeMOSFET for pixel switching and the P-type doping layer of semiconductorregion 8 as one electrode of the holding capacitance, an N-type wellregion 2, a P-channel-type MOSFET for pixel switching and a N-typedoping layer of semiconductor region as one electrode of the holdingcapacitance are also available. In this case, it is preferable that agiven voltage V_(DD) is applied to the N-type doping layer as oneelectrode of the holding capacitance as in the P-type well region. It ispreferred that the given voltage VDD be a higher voltage of the powervoltages since it applies a voltage to the N-type well region. Forexample, when a voltage of image signals applied to the source and drainin the MOSFET for pixel switching is 5 volts, it is preferable that thegiven voltage V_(DD) also be 5 volts.

A high voltage, e.g. 15 volts, is applied to the gate electrode 4 a ofthe MOSFET for pixel switching, whereas logic circuits, such as a shiftresistor, in the peripheral circuit, are driven by a low voltage, e.g. 5volts (but a part of the peripheral circuit, for example a circuit forapplying a scanning signal to the gate line is driven at 15 volts). Itis conceivable that the thickness of a gate insulating film in a FET asa peripheral circuit which is driven at 5 volts is lower than that of agate insulating film of an FET for pixel switching (by forming the gateinsulating film by another process or by etching the surface of the gateinsulating film of the FET in the peripheral circuit) in order toimprove the response of the FET in the peripheral circuit and increasethe operation rate of the peripheral circuit (in particular, a shiftresistor in a driving circuit at the data line side requiring high speedscanning). When such a technology is applied, the thickness of the gateinsulating film of the FET as a constituent of the peripheral circuitcan be reduced to approximately one third to one fifth the thickness ofthe gate insulating film of the FET for pixel switching (for example, 80to 200 angstroms) in view of voltage resistance.

The driving waveform in the first embodiment has a shape as shown inFIG. 8. In the drawing, V_(G) represents scanning signals applied to thegate electrode of the MOSFET for pixel switching, the time period t_(1H)represents a selection time period (scanning time period) to lead theMOSFET of the pixel and the time period other than that is anon-selection time period so as not to lead MOSFET of the pixel.Further, V_(d) represents the maximum amplitude of the image signalsapplied to the data line, V_(C) represents a central voltage of theimage signals, and LC-COM represents a common voltage applied to theopposing (common) electrode formed on the opposing substrate facing thereflective electrode substrate.

The voltage applied between the electrodes of the holding capacitor isdetermined by the difference between the image signal voltage V_(d)applied to the data line as shown in FIG. 8 and a given voltage V_(ss),such as 0 volts, applied to the P-type semiconductor region 8. Thedifference between the image signal voltage V_(d) and the centralvoltage V_(C) of the image signal, i.e., approximately 5 volts, is,however, sufficient for the voltage difference which is to be applied tothe holding capacitor (the common voltage LC-COM applied to the opposing(common) electrode 33 provided on the opposing substrate of the liquidcrystal panel in FIG. 6 is shifted by ΔV from V_(C), whereas the voltageactually applied to the pixel electrode is also shifted by ΔV andbecomes V_(d)-ΔV. The first embodiment therefore permits that the dopingregion 8 forming one terminal of the holding capacitor is set to bereverse polarity to the well (N-type for the P-type well) and it isconnected to a voltage of near V_(C) or LC-COM at the periphery of thepixel region so as to hold a voltage different from the well voltage(for example, V_(ss) for the P-type well). By simultaneously forming theinsulating film 9 b just below the polysilicon or metal silicide layeras one electrode 9 a of the holding capacitor with the gate insulatingfilm of the FET forming a peripheral circuit, not the gate insulatingfilm of the FET for pixel switching, the thickness of the insulatingfilm in the holding capacitor can be reduced to one third to one fifthcompared to the above-mentioned embodiment and the capacitance can beincreased by three to five times.

FIG. 1( b) is a cross-sectional view (cross-section II-II in FIG. 3) ofthe periphery of the pixel region in the first embodiment in accordancewith the present invention. The drawing shows a configuration of asection in which the doping region 8 extending in the scanning directionof the pixel region (pixel line direction) is connected to a givenvoltage (V_(ss)). Identification number 80 represents a P-type contactregion which is formed by the same step as the source/drain region ofthe MOSFET in the peripheral circuit, in which impurities having thesame conductivity type are ion-implanted after the formation of the gateelectrode into the doping region 8 which is formed before the formationof the gate electrode. The contact region 80 is connected to the line 70through the contact hole 71 to apply a constant voltage V_(ss). Theupper face of the contact region 80 is also shielded with a lightshielding film 14′ composed of a third metal layer.

FIG. 2 is a cross-sectional view of an embodiment of a CMOS circuitdevice forming a peripheral circuit, e.g. a driving circuit, outside thepixel region. In FIG. 2, the positions having the same numbers as FIG. 1represent the metal layer, insulating film and semiconductor regionwhich are formed by the same step.

In FIG. 2, identification numbers 4 a and 4 a′ represent gate electrodesof an N-channel MOSFET and a P-channel MOSFET forming a peripheralcircuit (CMOS circuit) such as a driving circuit, respectively,identification numbers 5 a (5 b) and 5 a′ (5 b′) represent an N-typedoping region and a P-type doping region, respectively, as theirrespective source and drain regions, and identification numbers 5 c and5 c′ represent their respective channel regions. The contact region 80for supplying a constant voltage V_(ss) to the P-type doping region 8 asone electrode of the holding capacitor in FIG. 1 is formed by the samestep as the P-type doping region 5 a′ (5 b′) as the source (drain)region of the P-channel MOSFET. Identification numbers 27 a and 27 crepresent source electrodes formed by the first metal layer andconnected to the power voltage (any one of 0 volt, 5 volts and 15volts), and identification number 27 b represents a drain electrodeformed by the first metal layer. Identification number 32 a represents awiring layer composed of the second metal layer and is used as a wirefor connecting between the devices forming a peripheral circuit.Identification number 32 b also represents a power wiring layer composedof the second metal layer and acts as a light shielding film. The lightshielding film 32 b can be connected to any one of V_(C), LC-COM, powervoltage, a constant voltage, e.g. 0 volt, and a variable voltage. Theshielding film formed from the same layer as the wiring layers 32 a and32 b may be in a floating voltage (non-applied voltage) state byseparating with the wiring layers 32 a and 32 b. Identification number14′ represents a third metal layer which is used as a light shieldingfilm in the peripheral circuit and prevents erroneous operation of theperipheral circuit due to unstable voltage in the semiconductor regionwhich is caused by carriers formed during light transmittance in thesemiconductor region of the peripheral circuit. Accordingly, theperipheral circuit is also shielded from light by the second and thirdmetal layers.

As described above, the passivation film 17 in the peripheral circuitmay be a protective film composed of a silicon nitride film or adouble-layered film of silicon oxide and silicon nitride thereon, inwhich the silicon nitride protective film is superior to the siliconoxide film as the passivation film in the pixel region. The source/drainregion of the MOSFET forming the peripheral circuit of this embodimentmay be formed by a self-alignment process, although it not limited tothis. The source/drain region of each MOSFET may have a LDD (lightlydoped drain) structure or a DDD (double doped drain) structure. It ispreferred that the FET for pixel switching have an offset structure inwhich the gate electrode is distant from the source/drain region, takinginto consideration that the FET for pixel switching is driven by a highvoltage and the leakage current must be prevented.

FIG. 4 shows a preferred embodiment of an edge structure of a reflectingelectrode (pixel electrode) substrate. In FIG. 4, the parts having thesame identification numbers represent the layers and semiconductorregions formed by the same steps.

As shown in FIG. 4, the edge of the laminate composed of the insulatinginterlayer and the metal layer and its side wall has a monolithicprotective structure in which a silicon nitride film 18 is formed on thesilicon oxide passivation film 17 which covers the pixel region and theperipheral circuit. The edge corresponds to each of the edges ofsubstrates (semiconductor chip) which are formed on a silicon wafer andseparated by dicing along the scribe lines. The lower right portion ofthe step in FIG. 4 corresponds to the scribe region.

Since the upper section and side wall of the substrate are covered withthe silicon nitride protective film at the edge, water and the like willbarely penetrate from the edge, durability is improved and the yield isimproved due to reinforcement of the edge. In this embodiment, a sealingmaterial 36 for encapsulating the liquid crystal is provided on themonolithic protective structure which is perfectly planarized. Thedistance to the opposing substrate therefore can be maintained constantregardless of variation of the thickness whether the insulatinginterlayer and the metal layer are present or not. Since the aboveconfiguration permits a single-layered silicon oxide protective film onthe reflecting electrode forming a pixel electrode, it can suppress adecrease in reflectance and dependence of the reflectance on thewavelength.

As shown in FIG. 4, in this embodiment, the third metal layer 14′ is thesame as the layer 14 which is used as the light shielding film in theperipheral circuit region and the reflection electrode of the pixel, andit is connected to the predetermined voltage through the second andfirst metal layers 12′ and 7′ and fixed to the substrate voltage. Alsothe second metal layer 12′ or the first metal layer 7′ may be extendedunder the sealing material 36 instead of the third metal layer 14′ to beused as a layer for fixing the voltage. This is capable of preventingstatic electricity during the formation of the liquid crystal substrateand liquid crystal panel and after the formation of the liquid crystalpanel.

FIG. 5 shows another embodiment in accordance with the presentinvention. FIG. 5 is a cross-sectional view along line I-I in the planarlayout in FIG. 3, as in FIG. 1. In FIG. 5, the sections having the sameidentification numbers as FIGS. 1 and 2 represent the layers and thesemiconductor regions formed by a similar process to the embodimentshown in these drawings. In this embodiment, a silicon nitride film 13 bis formed under the insulating interlayer 13 a composed of the TEOS film(partly including a remaining SOG film during etching) between thereflecting electrode 14 and the light shielding layer 12 thereunder.Alternatively, a silicon nitride film 13 b may be formed on the TEOSfilm 13 a. The use of a configuration having an additional siliconnitride film inhibits penetration of water and thus improves moistureresistance.

The thickness of the passivation film on the reflecting electrode issimilar to the embodiment shown in FIG. 1.

FIG. 16 shows another embodiment in accordance with the presentinvention. FIG. 16 is a cross-sectional view along line I-I in theplanar layout in FIG. 3, as in FIG. 1. In FIG. 16, the sections havingthe same identification numbers as FIGS. 1 and 2 represent the layersand the semiconductor regions formed by a similar process to theembodiment shown in those drawings. In this embodiment, a siliconnitride film 13 b is formed on the insulating interlayer 13 a composedof the TEOS film (partly including a remaining SOG film during etching)between the reflecting electrode 14 and the metal layer thereunder asthe shielding layer 12. The silicon nitride film 13 a can be planarizedby a CMP process or the like. The formation of the silicon nitride filmdecreases openings in the silicon nitride section compared to theembodiment in FIG. 5, and prevents penetration of water, resulting infurther improvement in moisture resistance. The space between thereflecting electrode and the adjacent electrode is formed of aprotective insulating film 17 and the silicon nitride film 13 b. Sincethe refractive index of the silicon nitride is 1.9 to 2.2 and higherthan the refractive index 1.4 to 1.6 of the silicon oxide used in theprotective insulating film 17, the incident light on the protectiveinsulating film 17 from the liquid crystal side is reflected at theinterface with the silicon nitride film 13 b because of the differenceof the refractive indices. Since the light incident on the interlayer isdecreased, unstable voltage in the semiconductor region caused bycarriers which are formed by light transmittance in the semiconductorregion are prevented.

In this embodiment, the silicon nitride film 13 b may be formed afterplanarization of the insulating interlayer 13 a composed of the TEOSfilm by a CMP process or the like. In general, a film having a thicknessof 8,000 to 12,000 angstroms which corresponds to local steps must bedeposited by, for example, a CMP process in order to offset the localsteps. The silicon nitride film used in 13 b generally causes a highstress on the lower film as its thickness increases. In this embodiment,since the insulating interlayer 13 a is planarized by polishing by meansof a CMP process and the silicon nitride film 13 b is formed thereon,the thickness of the silicon nitride film 13 b deposited by a CMPprocess or the like can be reduced, and thus the stress of the siliconnitride film 13 b is reduced. Since the space between the reflectingelectrode 14 and the adjacent reflecting electrode is composed of theprotective insulating film 17 and silicon nitride film 13 b in thiscase, the light incident on the interlayer decreases, and unstablevoltage in the semiconductor region due to carriers formed by lighttransmittance in the semiconductor region is prevented. It is preferablein this embodiment that the thickness of the silicon nitride be 2,000 to5,000 angstroms. A thickness of 2,000 angstroms or more improvesmoisture resistance of the silicon nitride film 13 b, whereas athickness of 5,000 angstroms or less decreases the etching depth of thecontact hole 16, permits ready etching and relaxes the stress on thelower film.

The thickness of the passivation film on the reflecting electrode is thesame as the embodiment in FIG. 1.

FIG. 6 is a planar layout of an entire liquid crystal panel substrate(reflection electrode substrate) in which the above-mentioned embodimentis applied.

As shown in FIG. 6, in this embodiment a light shielding film 25 isprovided in order to shield the light incident on the peripheralcircuits provided on the periphery of the substrate. The peripheralcircuits are provided on the periphery of the pixel region 20 in which amatrix of the pixel electrodes is disposed, and include a data linedriving circuit 21 for supplying image signals to the data line 7 inresponse to the image data, a gate line driving circuit 22 forsequentially scanning gate lines 4, an input circuit for reading theimage data from the outside through the pad region 26, and a timingcontrol circuit 24 for controlling these circuits. These circuits areformed by combining active devices or switching devices composed ofMOSFETs formed by the same step as or a different step to the MOSFET forswitching the pixel electrodes and loading devices, such as resistorsand capacitors.

In this embodiment, the light shielding film 25 is composed of the thirdmetal layer which is formed by the same step as the pixel electrode 14shown in FIG. 1 so as to apply a given voltage, e.g. a power voltage,the central voltage V_(C) of the image signal or a common voltageLC-COM. Application of the given voltage to the light shielding film 25can reduce reflection compared to a floating voltage and other voltages.The light shielding film 25 may be in a floating voltage (non-appliedvoltage) state so that the light shielding film 25 will not apply avoltage to the liquid crystal 37. Reference numeral 26 represents a padused for supplying the power voltage or a pad region provided with aterminal.

FIG. 7 is a cross-sectional view of a reflection liquid crystal panelusing the above-mentioned liquid crystal panel substrate 31. As shown inFIG. 7, a supporting substrate 32 composed of glass or ceramic is bondedto the back surface of the liquid crystal panel substrate 31 with abonding agent. A glass substrate 35 at the incident side having acounter electrode (common electrode) composed of a transparent electrode(ITO) for applying a common voltage LC-COM is opposed to the frontsurface of the liquid crystal panel substrate 31 at an adequatedistance, and a well known TN (twisted nematic) liquid crystal or a SH(super homeotropic) liquid crystal 37 in which the liquid crystalmolecules are substantially vertically aligned in a non-voltage appliedstate is encapsulated into a gap formed by sealing the periphery of thesubstrates with a sealing material 36 to form a liquid crystal panel 30.The position of the sealing material is determined so that the padregion 26 is present outside the sealing material 36.

The light shielding film 25 on the peripheral circuits face the counterelectrode 33 through the liquid crystal 37. Since the LC common voltageis applied to the counter electrode 33 when the LC common voltage isapplied to the light shielding film 25, no direct current voltages areapplied to the liquid crystal disposed therebetween. As a result, liquidcrystal molecules are always twisted by approximately 90 degrees in theTN liquid crystal or always vertically aligned in the SH liquid crystal.

In this embodiment, since the liquid crystal panel substrate 31 composedof the semiconductor substrate is bonded to the supporting substrate 32composed of glass or ceramic at the back surface with a bonding agent,the strength is significantly enhanced. As a result, when these arebonded to the opposing substrate after the supporting substrate 32 isbonded to the liquid crystal panel substrate 31, the gap of the liquidcrystal layer is equalized over the entire panel.

The above description includes a configuration of a reflective liquidcrystal panel substrate using a semiconductor substrate and a liquidcrystal panel using the same. A configuration of a reflective liquidcrystal panel substrate using an insulating substrate will now bedescribed.

FIG. 17 is a cross-sectional view of a configuration of a pixel in areflective liquid crystal panel substrate. FIG. 17 is a cross-sectionalview along line I-I in the planar layout in FIG. 3, as in FIG. 1. Inthis embodiment, a TFT is used as a transistor for switching pixels. InFIG. 17, the sections having the same identification numbers as FIGS. 1and 2 represent the layers and the semiconductor regions having the samefunctions as in those drawings. Identification number 1 represents aquartz or non-alkaline glass substrate, single-crystal, polycrystallineor amorphous silicon film, regions 5 a, 5 b, 5 c and 8 are formed on theinsulating substrate, and insulating films 4 b and 9 b having a doublelayer structure composed of a silicon oxide film formed by thermaloxidation and a silicon nitride film formed thereon by a CVD process areformed on the silicon film. An N-type impurity is doped in the regions 5a, 5 b and 8 of the silicon film before the formation of the uppersilicon nitride film among the insulating film 4 b to form a sourceregion 5 a and a drain region 5 b of the TFT and an electrode region 8of the holding capacitor. A wiring layer composed of polysilicon or ametal silicide is formed as a gate electrode 4 a of the TFT and theother electrode 9 a of the holding capacitor is formed on the insulatingfilm 4 b. As described above, the TFT comprising the gate electrode 4 a,the gate insulating film 4 b, the channel 5 c, the source 5 a and thedrain 5 b and the holding capacitor comprising the electrodes 8 and 9and the insulating film 9 b are formed.

A first insulating interlayer 6 composed of silicon nitride or siliconoxide is formed on the wiring layers 4 a and 9 a, and a source electrode7 a which is connected to the source region 5 a through a contact holeformed in the insulating film 6 is formed of a first metal layercomposed of aluminum. A second insulating interlayer 13 having adouble-layer structure composed of a silicon oxide film and a siliconnitride film is formed on the first metal layer. The second insulatinginterlayer 13 is planarized by a CMP process and a pixel electrode 14,as a reflection electrode, composed of aluminum is formed thereoncorresponding to each pixel. The electrode region 8 of the silicon filmis electrically connected to the pixel electrode 14 through a contacthole 16. Such a connection is achieved by embedding a connecting plug 15composed of a high melting point metal, such as tungsten, as in FIG. 1.

As described above, since the reflecting electrode is formed above theTFT and holding capacitor formed on the insulating substrate, the pixelelectrode region is expanded and the holding capacitor has a large areabelow the reflecting electrode as in the planar layout in FIG. 3. A highaperture ratio (high reflectance) therefore can be achieved even in ahigh definition panel (having smaller pixels) and an applied voltage canbe sufficiently retained in each pixel, resulting in stable driving.

A passivation film 17 composed of a silicon oxide film is formed on thereflecting electrode 14, as in the above-mentioned embodiments. Thethickness of the passivation film 17 is similar to that in thoseembodiments, and a reflective liquid crystal panel substrate having asmall variation of reflectance with the wavelength of the incident lightcan be obtained. A comprehensive configuration of the liquid crystalpanel substrate and a configuration of the liquid crystal panel aresimilar to those in FIGS. 6 and 7.

In FIG. 17, no insulating interlayer 11 and light shielding layer 12 areprovided unlike FIG. 1. These layers can also be provided as in FIG. 1in order to prevent leakage of the incident light from the gap to theadjacent pixel on the TFT. If incident light from the bottom of thesubstrate is anticipated, a light shielding layer may be provided underthe silicon films 5 a, 5 b and 8. Although the drawing includes a topgate type in which the gate electrode is provided above the channel, abottom gate type in which a gate electrode is previously formed and asilicon film as a channel is provided thereon through a gate insulatingfilm is also available. Also a double layer structure composed of asilicon oxide film and a silicon nitride film in the peripheral circuitregion as in FIG. 4 can improve moisture resistance.

FIG. 9 shows an example of electronic devices using the liquid crystalpanels in accordance with the present invention, and is a planarschematic diagram of the main section of a projector (projection displaydevice) using a reflective liquid crystal panel in accordance with thepresent invention as a light valve. FIG. 9 is a cross-sectional view ofan XZ plane which passes through the center of an optical element 130.This projector includes a light source 110 provided along the systemlight axis L (111 represents a lamp and 112 represents a reflector), anintegrated lens 120, a polarizing device 130, a polarizing illuminator100 including the polarizing device 130, a polarized beam splitter 200which reflects a S-polarized light beam emerging from the polarizingilluminator 100 by a S-polarized light beam reflecting face 201, adichroic mirror 412 which separates the blue (B) light component fromthe light reflected on the S-polarized light beam reflecting face 201 ofthe polarized beam splitter 200, a reflective liquid crystal light valve300B modulating the separated blue (B) light, a dichroic mirror 413which separates a red (R) light component from the light beam notcontaining the blue light component, a reflective liquid crystal lightvalve 300R modulating the separated red (R) light, a reflective liquidcrystal light valve 300G modulating the residual green (G) light passedthrough the dichroic mirror 413, and a projection optical system 500which includes a projection lens projecting a synthesized light on ascreen 600 in which the modulated light beams from the three reflectionliquid crystal light valves 300R, 300G, and 300B are combined throughthe dichroic mirrors 412 and 413 and the polarized beam splitter 200.These three reflective liquid crystal valves 300R, 300G and 300B areprovided with the above-mentioned liquid crystal panels, respectively.

The random polarized light beams emerging from the light source 110 aredivided into a plurality of intermediate light beams by the integratedlens 120, converted to single-polarization light beams (S-polarizedlight beam) substantially having a polarized light direction with thepolarizing device 130 which has a second integrated lens at the lightincident side, and are incident on the polarized beam splitter 200. TheS-polarized light beams emerging from the polarizing device 130 arereflected from the S-polarized light beam reflecting face 201 of thepolarized beam splitter 200, the blue (B) light beam among the reflectedlight beams is reflected on the blue light reflecting layer of thedichroic mirror 412 and modulated by the reflection liquid crystal lightvalve 300B. The red (R) light beam among the light beams passed throughthe blue light reflecting layer of the dichroic mirror 412 is reflectedon the red light reflecting layer of the dichroic mirror 413 andmodulated by the reflective liquid crystal light valve 300R.

Further, the green (G) light beam passed through the red lightreflecting layer of the dichroic mirror 413 is modulated by thereflective liquid crystal light valve 300G. In such a manner, the colorlight beams modulated by the reflective liquid crystal light valves300R, 300G and 300B are combined by the dichroic mirrors 412 and 413 andthe polarized beam splitter 200, and the combined light is projectedthrough the projection optical system 500.

The reflective liquid crystal panel used in the reflective liquidcrystal light valves 300R, 300G and 300B contains a TN liquid crystal(longitudinal axes of liquid crystal molecules are substantially alignedin the direction parallel to the panel substrate when no voltage isapplied) or a SH liquid crystal (longitudinal axes of liquid crystalmolecules are substantially aligned in the direction perpendicular tothe panel substrate when no voltage is applied).

When a TN liquid crystal is used, in a pixel (OFF pixel) in which avoltage applied to the liquid crystal layer intervened between thereflecting electrode of the pixel and the common electrode of theopposing substrate is lower than a threshold voltage, the incident colorlight is elliptically polarized in the liquid crystal layer, isreflected from the reflecting electrode and emerges from the liquidcrystal layer in which the polarization axis of the emerging light isshifted by 90 degrees from the incident light and ellipticallypolarized. On the other hand, in a pixel (ON pixel) in which a voltageis applied to the liquid crystal layer, the incident color light reachesthe reflective electrode without polarization, is reflected and emerged,in which the emerging light has the same polarization axis as theincident light. Since the alignment angle of the liquid crystal moleculeof the TN liquid crystal varies in response to the voltage applied tothe reflective electrode, the angle of the polarization axis of thereflected light in relation to the incident light varies in response tothe voltage applied to the reflective electrode through the transistorin the pixel.

When a SH liquid crystal is used, in a pixel (OFF pixel) in which thevoltage applied to the liquid crystal layer is lower than a thresholdvoltage, the incident color light reaches the reflective electrodewithout polarization, is reflected and emerges, in which the emerginglight has the same polarization axis as the incident light. On the otherhand, in a pixel (ON pixel) in which a voltage is applied to the liquidcrystal layer, the incident color light is elliptically polarized in theliquid crystal layer, reflected on the reflective electrode and emergesfrom the liquid crystal layer in which the polarization axis of theemerging light is shifted by 90 degrees from the incident light and theemerging light is elliptically polarized. Since the alignment angle ofthe liquid crystal molecules of the SH liquid crystal varies in responseto the voltage applied to the reflective electrode as in the TN liquidcrystal, the angle of the polarization axis of the reflected light inrelation to the incident light varies in response to the voltage appliedto the reflective electrode through the transistor in the pixel.

Among the color light beams reflected from pixels in these liquidcrystal panels, the S-polarized light component does not pass throughthe polarized beam splitter 200 which reflects the S-polarized light andtransmits P-polarized light. The light beams passed through thepolarized beam splitter 200 form an image. The projected image is anormally-white display when a TN liquid crystal is used in the liquidcrystal panel because the reflected light beams in OFF pixels reach theprojection optical system 500 and the reflected light beams in ON pixelsdo not reach the lens, and a normally-black display when a SH liquidcrystal is used because the reflected light beams in OFF pixels do notreach the projection optical system and the reflected light beams in ONpixels reach the projection optical system 500.

Since reflective liquid crystal panels permit larger pixel electrodescompared to transmission active matrix liquid crystal panels, highreflectance is achieved, high density images can be projected at highcontrast and projectors can be miniaturized.

As shown in FIG. 7, the peripheral circuit section of the liquid crystalpanel is covered with the light shielding film, and the same voltage(for example, the LC common voltage; if the LC common voltage is notused, the peripheral counter electrode is separated from the counterelectrode in the pixel) is applied to the section and the counterelectrode formed at the position in which the opposing substrate isopposed. Almost zero volts is therefore applied to the liquid crystalintervened between them and the liquid crystal is the same as an OFFstate. As a result, in the TN liquid crystal panel the periphery of theimage region exhibits an entire white display in response to thenormally-white display, whereas in the SH liquid crystal panel theperiphery of the image region exhibits an entire black display inresponse to the normally-black display.

Further satisfactory results are obtained when the silicon oxide formingthe passivation film of the light valve 300R as the first reflectiveliquid crystal panel modulating red light separated by the polarizedbeam splitter 200 as a color separation means which separates the lightfrom the light source 110 into three primaries has a thickness in arange of 1,300 to 1,900 angstroms, the silicon oxide forming thepassivation film of the light valve 300G as the second reflective liquidcrystal panel modulating green light has a thickness in a range of 1,200to 1,600 angstroms, and the silicon oxide forming the passivation filmof the light valve 300B as the third reflective liquid crystal panelmodulating blue light has a thickness in a range of 900 to 1,200angstroms.

In accordance with the above-mentioned embodiment, a voltage applied toeach of pixels in the reflective liquid crystal panels 300R, 300G and300B is sufficiently retained and the pixel electrode has asignificantly high reflectance, resulting in clear projected images.

FIG. 15 includes views illustrating appearances of electronic devicesusing the reflection liquid crystal panels in accordance with thepresent invention. In these electronic devices, the reflection liquidcrystal panel is used as a direct viewing-type reflection liquid crystalpanel, not as a light valve which is used together with a polarized beamsplitter. The reflecting electrode must therefore not be a perfectmirror surface and preferably has adequate unevenness. Otherconfigurations are basically the same as the light valve.

FIG. 15( a) is an isometric view of a portable telephone. Identificationnumber 1000 represents a portable telephone main body, andidentification number 1001 represents a liquid crystal display using areflective liquid crystal panel in accordance with the presentinvention.

FIG. 15( b) shows a watch-type electronic device. Identification number1100 is an isometric view of a watch main body. Identification number1101 represents a liquid crystal display using a reflective liquidcrystal panel in accordance with the present invention. Since the liquidcrystal panel has high definition pixels compared to conventional watchdisplays and is capable of displaying television images, a watch-typetelevision can be achieved.

FIG. 15( c) shows a portable information processing unit, e.g. a wordprocessor or a personal computer. Identification number 1200 representsan information processing unit, identification number 1202 represents aninput section such as a keyboard, identification number 1206 representsa display using a reflective liquid crystal panel in accordance with thepresent invention, and identification number 1204 represents aninformation processing unit main body. Since these electronic devicesare driven by batteries, the use of the reflective liquid crystal panelhaving no light source lamp can lengthen the battery life. Since theperipheral circuits can be stored in the panel substrate, significantreduction of parts, and weight and size reduction can be achieved.

In the above-mentioned embodiments, although a TN type and a homeotropicalignment SH type are exemplified as a liquid crystal of the liquidcrystal panel, other types of liquid crystals are also available.

As described above, a reflective liquid crystal panel substrate inaccordance with the present invention is provided with a passivationfilm, and thus has improved reliability. The use of a silicon oxide filmhaving a thickness of 500 to 2,000 angstroms as the passivation reducesdependence of reflectance of the pixel electrode on variation of thethickness. In particular, the silicon oxide film having a thickness of500 to 2,000 angstroms exhibits slight dependence of the reflectance onthe wavelength and thus can reduce variation of the reflectance.

The thickness of the silicon oxide film as the passivation film is setto an adequate range in response to the wavelength of the incidentlight, e.g. 900 to 1,200 angstroms for a pixel electrode reflecting bluelight, 1,200 to 1,600 angstroms for a pixel electrode reflecting greenlight, and 1,300 to 1,900 angstroms for a pixel electrode reflecting redlight. Variation of the reflectance in each color can therefore besuppressed to 1% or less. As a result, reliability of the liquid crystalpanel can be improved, and the image quality of a projection displaydevice using the reflective liquid crystal panel as a light valve can beimproved.

Since the thickness of the silicon oxide film as the passivation film isdetermined in response to the thickness of the alignment film formedthereon and the thickness of the alignment film is set to a range of 300to 1,400 angstroms, variation of the refractive index of the liquidcrystal can be effectively prevented.

In a reflective liquid crystal panel in which a pixel region comprisinga matrix of pixel electrodes and peripheral circuits, such as a shiftregister and a control circuit, provided outside the pixel region areformed on the same substrate, a passivation film composed of a siliconoxide film is formed above the pixel region and a passivation filmcomposed of a silicon nitride film is formed above the peripheralcircuits. The use of the silicon nitride film above the peripheralcircuits further secures protection of the peripheral circuits andimproves reliability.

A silicon nitride film is provided as an insulating interlayer betweenthe reflective electrode and a metal layer thereunder instead of thepassivation film above the reflective electrode or together with thepassivation film composed of the silicon oxide film. The moistureresistance is therefore improved, a MOSFET for pixel switching and aholding capacitor can be prevented from corrosion due to water or thelike.

A monolithic protective structure in which a silicon nitride film isformed on a passivation film composed of a silicon oxide film isprovided over the edge and side wall of a laminate of an insulatinginterlayer formed at the periphery of the pixel region and a metal layershielding the periphery. The waterproof property at the edge of theliquid crystal panel in which water readily penetrates is thereforeimproved and durability is also improved due to its reinforcementeffect.

1. A substrate for a liquid crystal panel, comprising: a pixel regionhaving a reflecting electrode formed on the substrate and a switchingelement formed under the reflecting electrode; a periphery regionarranged in a periphery of the pixel region and having a peripherycircuit, a first light shielding film located in the pixel region, thefirst light shielding film formed by metal material and interposedbetween the reflecting electrode and the switching element; a secondlight shielding film located in the periphery region over the peripherycircuit, the second light shielding film being formed in the same layeras the first light shielding film; and a third light shielding filmlocated over the second light shielding, film, the third light shieldingfilm being formed in the same layer as the reflecting electrode, thesecond light shielding film electrically coupling between devicesforming the periphery circuit.
 2. The substrate for a liquid crystalpanel according to claim 1, films in a same layer formed from a samemetal material.
 3. An electronic device comprising a liquid crystalpanel with a substrate according to claim 1 as a display section.
 4. Aprojection display device, comprising: the electronic device accordingto claim 3, a light source, the liquid crystal modulating the light fromthe light source; and a projection lens for projecting the lightmodulated by the liquid crystal panel.